In radar applications, it is common to send a signal away from a radar station along a particular direction, receive a reflected signal at the radar station along the particular direction, and use the time of flight between the sent and received signals to determine a distance away from the radar station of a particular reflecting object. The sent signal can be pulsed, and can be sent with a randomly-varying wavelength, in order to avoid detection.
Many current radar systems use active electronically scanned arrays (AESAs). A typical AESA system includes an array of modules that can both transmit and receive signals. The AESA system can steer the outgoing signals by controlling the times at which the modules emit their respective signals. The outgoing signals effectively form a wavefront, and the sensitivity of the AESA is greatest along a direction that is perpendicular to the wavefront; this sensitivity is analogous to a condition of constructive interference for optical phenomena.
One potential drawback to AESAs is that they can be complex and expensive. For instance, a typical AESA system can include multiple transmission lines, phase shifter and RF front ends.